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  <div id="layout-content"><div id="function.atan" class="refentry">
 <div class="refnamediv">
  <h1 class="refname">atan</h1>
   <p class="verinfo">(PHP 4, PHP 5, PHP 7, PHP 8)</p><p class="refpurpose"><span class="refname">atan</span> &mdash; <span class="dc-title">反正切</span></p>

 </div>
 <div class="refsect1 description" id="refsect1-function.atan-description">
  <h3 class="title">说明</h3>
  <div class="methodsynopsis dc-description">
   <span class="methodname"><strong>atan</strong></span>(<span class="methodparam"><span class="type">float</span> <code class="parameter">$num</code></span>): <span class="type">float</span></div>

  <p class="para rdfs-comment">
   返回 <code class="parameter">num</code> 的反正切值，单位是弧度。<span class="function"><strong>atan()</strong></span> 是
   <span class="function"><a href="function.tan.html" class="function">tan()</a></span> 的反函数，它的意思是在
   <span class="function"><strong>atan()</strong></span> 范围里的每个值都是
   <code class="literal">a==tan(atan(a))</code>。
  </p>
 </div>

 <div class="refsect1 parameters" id="refsect1-function.atan-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>
    
     <dt>
<code class="parameter">num</code></dt>

     <dd>

      <p class="para">
       要处理的参数
      </p>
     </dd>

    
   </dl>

  </p>
 </div>

 <div class="refsect1 returnvalues" id="refsect1-function.atan-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   <code class="parameter">num</code> 的反正切弧度。
  </p>
 </div>

 <div class="refsect1 seealso" id="refsect1-function.atan-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="function.tan.html" class="function" rel="rdfs-seeAlso">tan()</a> - 正切</span></li>
    <li class="member"><span class="function"><a href="function.atanh.html" class="function" rel="rdfs-seeAlso">atanh()</a> - 反双曲正切</span></li>
    <li class="member"><span class="function"><a href="function.asin.html" class="function" rel="rdfs-seeAlso">asin()</a> - 反正弦</span></li>
    <li class="member"><span class="function"><a href="function.acos.html" class="function" rel="rdfs-seeAlso">acos()</a> - 反余弦</span></li>
   </ul>
  </p>
 </div>

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